Select the outermost contour of an imported SVG
I went for the solution to iterate over the imported object. For reference the import routine, to see how the SVG gets imported in detail. The data is avail in the objects data.spline collection then.

The correct function relies on that the remaining element has to be the first object in the collection (key not in 0). At least for exported SVGs from corel draw this is true, I guess for others, too.

code snippet I use for now:

# remove all inner elements
svg_splines_collection=obj.data.splines
splineset_to_remove = [value for key, value in svg_splines_collection.items() if key not in (0,)]
for spline in splineset_to_remove:
    svg_splines_collection.remove(spline)


if someone comes up with a better solution I'd appreciate.